1. Field of the Invention
The invention relates to a sighting cap mountable on a housing of a laser beam transmitter which effects the rotation of the laser beam about a generally vertical axis of rotation, the cap being provided with diametrically opposed slots permitting the visual alignment of the housing, and hence the plane to be generated by the rotating laser beam, with a remote sighting post.
2. Background of the Invention
Apparatus employing a rotating laser beam for effecting surveying operations or the guidance and/or control of earth working implements disposed on the terrain over which the rotating laser beam is traversed, was first introduced in the late 1960's. See, for example, U.S. Pat. Nos. 3,588,249 to Studebaker, 3,865,491 to Hogan, 3,936,197 to Aldrink et al and U.S. Pat. No. 4,062,634 to Rando et al. Such devices commonly employed a generally vertically disposed laser beam generator mounted in a stationary housing which was connected to support legs by a transit-like adjusting mechanism, permitting the position of the vertical axis of the stationary housing or the generated laser beam to be conveniently adjusted. The actual rotation of the laser beam was accomplished by a rotating pentaprism that was journalled in the stationary housing for rotation about the vertical axis of the generated laser beam. The angular position of the reference plane generated by the rotating laser beam was then determined by the adjustment of the vertical axis of the generated laser beam or the stationary housing containing the laser beam generator.
Whenever it is desired that the plane of the rotating laser beam be disposed at an angle relative to the vertical other than 90.degree., and this is the most common situation encountered, it is necessary to effect the displacement of the rotational axis of the generated laser beam with respect to the vertical so that the resulting rotating laser beam occupies the desired non-horizontal plane.
In the past, the apparatus was first set up in the work area with the axis of the generated laser beam disposed in a true vertical position. Micrometer adjustment of the transit-type positioning mechanisms effecting the mounting of the laser beam generating apparatus or the stationary housing to the support legs would then produce a tilting of the housing by pre-calculated amounts along two horizontal axes to effect the disposition of the axis of the generated laser beam in a perpendicular position relative to the desired plane of rotation of the rotating laser beam. This method necessarily required some trigonometric calculation of the amount of micrometer adjustment of the transit-type positioning mechanism, or reference to a pre-calculated table, which had to be carried with the transmitter. If any change in the angularity of the rotating laser beam plane were desired, the reference to the calculation table and the micrometer adjustments would have to be repeated. Such procedures obviously are not advantageously employed in field operations.
It is also possible to set up two spaced beam detectors respectively defining the desired elevation of the rotating laser plane at two points remote from the location of the rotational axis of the rotating laser beam plane. The operator would then adjust the angular position of the rotational axis of the rotating laser beam to attempt to cause the resulting beam to traverse the center of each of the two beam detectors at the desired elevational position. Again, a time consuming procedure was involved and a minimum of two operators were required; one at the transmitter and another at the elevation markers.
In recent years, more sophisticated rotating laser beam transmitters have been commercially available from Laserplane Corporation of Dayton, Ohio, the most recent being marketed under the trademark "LASERLEVEL" Model 1045DSL transmitter. In this transmitter, the micrometer adjustments of the vertical axis of the laser beam generator and the rotating pentaprism are effected by two electrically powered motors which respectively effect adjustment of the rotational axis of the laser beam in two 90.degree. displaced vertical planes. Thus, if the desired angular relationship of the rotating laser beam plane with respect to two horizontal axes is known, the motors may be respectively actuated by push buttons contained on a hand held controller and the degree of angularity with respect to each of the two 90.degree. displaced axes will be indicated on a electronically actuated display panel located on the hand held controller.
Even with this sophisticated mechanism for selectively positioning the plane of a rotating laser beam over a range of desired angular relationships with respect to the true vertical, it is necessary to survey the work area to determine the location of the X and Y axes and the displacements of the desired laser beam plane relative to such axes. The laser beam transmitter is then located on the work area at a known position relative to the survey axes and the corresponding beam adjustment axes of the transmitter placed in parallel relationship to the survey axes. Inexpensive yet accurate means for effecting such alignment of the transmitter adjustment axes with the survey axes have not been heretofore available.